The present invention relates to a thrust bearing device and a motor equipped with the bearing device.
Japanese Unexamined Patent Publication No. Hei 5-15103 discloses an example of a thrust bearing device. In the bearing device disclosed in this publication, a rotating shaft or an output shaft of a motor is received at one end by a holder located in a gear case. A sleeve for receiving the radial force of the output shaft and a steel ball for receiving the axial force of the output shaft are arranged in the holder. The holder has a plurality of supporting legs extending toward the inner bottom face of the gear case. A cavity is present between the inner bottom face of the gear case and the holder. The gear case has a charging port communicating with the cavity.
Filler material is charged through the charging port into the cavity. The filler solidifies to position the output shaft in the axial direction and prevent backlash in the axial direction. Further, the supporting legs of the holder are embedded in the filler, and thus the holder is supported on the gear case and cannot rotate relative to the gear case. Therefore, the holder is not caused to rotate together with the output shaft.
The steel ball is held and enveloped by the holder. The steel ball and the holder contact one another over a large contact surface area. This increases the sliding resistance between the steel ball and the holder and the rotational resistance of the output shaft.
Although not specified in the publication, the holder is likely to be made of resin, because it has a relatively intricate configuration. However, a resin holder has poor durability, since it can be deformed by the frictional heat generated between the holder and the steel ball or by the axial force of the output shaft.
It is an object of the present invention to provide a thrust bearing device that is durable and that reduces the rotational resistance of a rotating shaft and a motor equipped with the bearing device.
To attain the above object, the present invention provides a thrust bearing device for a rotating shaft. The device has a housing containing a holding recess. A receiving plate is located in the holding recess to oppose an end face of the rotating shaft. The receiving plate defines, at a distal end thereof with respect to the rotating shaft, a charging cavity in the holding recess. A metallic ball is located in the holding recess between the end face of the rotating shaft and the receiving plate. The ball contacts the end face of the rotating shaft and the receiving plate. A resin material is charged into the charging cavity. Afterwards, the resin material solidifies to restrict the axial position of the rotating shaft. The receiving plate is made of a metal and makes point contact with the ball. The receiving plate is formed so that it does not rotate with respect to the solidified resin.
The present invention also provides a motor having a motor main body with a drive shaft and a decelerating mechanism for decelerating rotation of the drive shaft. The decelerating mechanism includes a housing, a worm shaft, which is located in the housing so that the worm shaft is connected to the drive shaft, and a thrust bearing device, which is located near a distal end of the worm shaft. The thrust bearing device contains a holding recess defined in the housing and a metallic receiving plate located in the holding recess to oppose a distal end face of the worm shaft. The receiving plate defines, at a distal end thereof with respect to the worm shaft, a charging cavity in the holding recess. A metallic ball is located in the holding recess between the distal end face of the worm shaft and the receiving plate. The ball contacts the distal end face of the worm shaft and the receiving plate. A resin material is charged into the charging cavity. Afterwards, the resin material solidifies to restrict the axial position of the worm shaft. The thrust bearing device also has connecting means for connecting the receiving plate to the solidified resin material and for preventing rotation of the receiving plate.